Rock bolt

ABSTRACT

An anchor device which includes a pipe ( 16 ), an elongate member ( 18 ) which is partly inside the pipe and which has an end ( 20 ) which protrudes from the pipe ( 16 ), and a restraining component ( 22 ) which is engaged with the protruding end ( 20 ). and wherein the pipe ( 16 ) and elongate member ( 18 ) are shaped with a plurality of formations, along their respective lengths, so that the elongate member ( 16 ) can only be withdrawn from the tubular member by deforming the elongate member( 18 ).

BACKGROUND OF THE INVENTION

This invention relates to an anchor device.

As used herein the expression “anchor device” designates a load carrying device which is capable of yielding in a controlled manner when the load on the device increases above a predetermined limit.

Without being restrictive in any way an anchor device, as defined, may be used as a rock bolt to reinforce a rock face or as a reinforcing element in a concrete structure such as a bridge or building.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a method of forming an anchor device which includes the steps of:

-   -   (a) locating an elongate member at least partly within a tubular         member; and     -   (b) simultaneously deforming the elongate member and the tubular         member at least at one location whereby withdrawal of the         elongate member from the tubular member is inhibited.

At least a portion of the elongate member and of the tubular member may be deformed into a substantially sinusoidal shape.

The elongate member and the tubular member may be deformed at each of a plurality of locations which are spaced from each other in a longitudinal direction of the elongate member.

The method may include the step of securing a restraining component to an end of the elongate member which extends from the tubular member.

The tubular member may be at least one pipe and the elongate member may be selected from the following: a rod and a cable.

The invention also provides an anchor device which includes a tubular member, and an elongate member at least partly inside the tubular member, the tubular member and the elongate member being shaped, in a complementary manner, at least at one location whereby withdrawal of the elongate member from the tubular member is inhibited.

The arrangement may be such that the elongate member can only be withdrawn from the tubular member by deforming the elongate member.

The anchor device may include a restraining component at an end of the elongate member which protrudes from the tubular member.

The elongate member may be any appropriate element or elements and, for example, may be selected from a rod and a cable.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further described by way of example with reference to the accompanying drawing which. depicts from the side and in cross section an anchor device according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

The accompanying drawing illustrates from the side and in cross section an anchor device 10, according to the invention, installed in a hole 12 which is formed in a rock face 14.

The anchor device includes an elongate tubular member 16 which is in the nature of a thin wall steel pipe and an elongate load bearing member 18 which is inserted into the pipe with one end 20 protruding from the pipe.

The member 18 may be a steel rod or a cable.

A restraining component 22 is secured to the protruding end 20 and bears against a load distributing washer 24 which in turn acts against a surface of the rock face 14 which surrounds the hole 12.

The restraining device varies according to the nature of the elongate member 18. For example if the elongate member is a steel rod then the protruding end 20 may be threaded and the restraining component 22, which is then in the nature of a nut, is threadedly engaged with the end 20. Alternatively if the member 18 is a cable or is formed from a number of wires then the restraining component 22 may be in the nature of a lug or ferrule which is crimped onto the protruding end in situ at an installation site.

The anchor device 10 is formed, under factory conditions, by inserting the elongate member 18 into the pipe 16 when the pipe is of a regular shape ie. is not deformed. The pipe, which encloses the elongate member over a substantial portion of the length of the elongate member, is placed in a suitable press and is deformed in one or a plurality of steps into the shape shown in the drawing. The deformed pipe has peaks and troughs with a generally smooth transition between each peak and adjacent trough thereby imparting to the pipe an overall generally sinusoidal shape.

The undulations or sinusoidal peaks are spaced apart by a distance 26 which varies according to requirement.

The hole 12 is formed in the rock face using any appropriate technique known in the art and the anchor device 10 is placed in the hole with the pipe 16 embedded in grout or other settable material 28 which fills the hole. The settable material is normally injected into the hole using any suitable placement apparatus after the pipe has been inserted into the hole.

If the restraining component 22 is a nut then the washer and the nut are engaged with the protruding end 20 after the settable material is injected into the hole through its mouth. On the other hand if the restraining component is in the nature of a lug or similar device which is applied under factory conditions to the protruding end then the load distribution washer 24 may initially be displaced slightly from the rock face 14 to allow the settable material to be injected into the hole through its mouth or, alternatively, the washer 24 may have an aperture or passage formed through it and the settable material may be injected through the aperture or passage into the hole 12.

Ideally, once the material 28 has set, the component 22 is advanced along the member 18 to prestress the member. This may however not be possible if the component is crimped under factory conditions to the end 20. It is preferable therefore to attach the component to the end 20 in situ, at the installation location.

When the anchor device is embedded in the settable material, the material, whether grout, resin or of a different type, bonds to the exterior surface of the pipe which is thereby held firmly in position.

If there is movement of the rock face relatively to the bulk of the rock in which the hole 12 is formed then the load which is carried by the member 18 increases. The member 18 is therefore placed under increasing tensile stress. The rock face 14 can only move however when the load carried by the member 18 is so high that the element is deformed through the sinusoidal passage which is defined by the pipe 16. It is evident that the point at which yielding takes place is dependent on a number of factors including the material from which the elongate member is made, the dimensions and shape of the member, the clearance between the member and the inner wall of the pipe, and the number, depth and spacing of the formations in the pipe and the member.

The elongate member slides through the pipe by deforming as it passes through the undulations to provide a controlled yielding action with the pipe remaining behind and fully embedded in the settable material. An appropriate lubricant may be applied to the elongate member, before it is inserted into the pipe. This helps to ensure that a smooth sliding action takes place as yielding occurs, particularly if the yield rate is high ie. when the member 18 moves very rapidly, for example during a seismic event.

The length of the anchor device may be substantial. This makes the anchor device suitable for use in reinforced concrete applications for example in bridges and structures. With this type of application the member 18 will generally be a cable or comprise a plurality of high tensile winds which may be helically twisted, at least slightly. The installation and operation of the anchor device, in a reinforced concrete application, for all practical purposes, are the same as what has been described hereinbefore with reference to the use of the anchor device in a body of rock except that the device is cast in position.

The pipe 16 is rigid and if the anchor device is made to a substantial length it may be difficult to install the device particularly in an underground situation or in a location in which there is limited space. To impart a degree of flexibility to the anchor then, as is shown more clearly in the inset drawing, the member 18 may be a cable and the pipe 16 may comprise a plurality of relatively smaller lengths 16A, 16B, ... which are separated from each other along the length of the cable by means of suitable spacers 30, which may be made from a flexible plastics material. Each individual pipe length is sinusoidally deformed, with the cable inside, in the manner which has been described and is fixed in position when it is embedded in the settable material. However, before installation, it is possible to bend or flex the anchor device, at least to a limited degree, by bending one pipe section to a limited extent relatively to an adjacent pipe section. The use of the spacers does not adversely affect the strength of the anchor device nor the yielding action thereof. 

1. A method of forming an anchor device which includes the steps of: (a) locating an elongate member at least partly within a tubular member; and (b) simultaneously deforming the elongate member and the tubular member at each of a plurality of locations which are spaced from each other in a longitudinal direction of the elongate member whereby withdrawal of the elongate member from the tubular member is inhibited to provide a controlled yielding action.
 2. A method according to claim 1 wherein at least a portion of the elongate member and a portion of the tubular member are deformed into a substantially sinusoidal shape.
 3. A method according to claim 1 wherein the elongate member and the tubular member are deformed to have peaks and troughs.
 4. A method according to claim 1 which includes the step of securing a restraining component to an end of the elongate member which extends from the tubular member.
 5. A method according to claim 1 wherein the tubular member includes at least one pipe.
 6. A method according to claim 1 wherein the elongate member is selected from the following: a rod and a cable.
 7. An anchor device which includes a tubular member, and an elongate member at least partly inside the tubular member, the tubular member and the elongate member being shaped, in a complementary manner, at each of a plurality of locations which are spaced from each other in a longitudinal direction of the elongate member whereby withdrawal of the elongate member from the tubular member is inhibited to provide a controlled yielding action.
 8. An anchor device according to claim 7 wherein the tubular member and the elongate member are so shaped that the elongate member can only be withdrawn from the tubular member by deforming the elongate member.
 9. An anchor device according to claim 7 which includes a restraining component at an end of the elongate member which protrudes from the tubular member.
 10. An anchor device according to claim 7 which includes a lubricant on the elongate member inside the tubular member.
 11. An anchor device according to claim 7 wherein the elongate member is selected from a rod and a cable.
 12. An anchor device according to any claim 7 wherein the tubular member includes a plurality of pipes through which the elongate member passes.
 13. An anchor device according to claim 12 wherein adjacent pipes are separated by flexible spacers.
 14. An anchor device which includes a pipe, an elongate member which is partly inside the pipe and which has an end which protrudes from the pipe, and a restraining component which is engaged with the protruding end, and wherein the pipe and elongate member are shaped with a plurality of sinusoidal formations, along their respective lengths, so that the elongate member can only be withdrawn from the tubular member by deforming the elongate member thereby to provide a controlled yielding action. 